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GEOGRAPHIC INFORMATION SERVICES (GIS)
GIS tasks
General purpose GISs essentially perform six processes or tasks:
Input
Before
geographic data can be used in a GIS it must be converted into a suitable
digital format. The process of converting data from analogue paper maps into
computer files is called digitizing. Modern GIS technology has the capability to
automate this process fully for large projects; smaller jobs may require some
manual digitizing.
Today many types of geographic data already exist in
GIS-compatible formats. These data can be obtained from data suppliers and
loaded directly into a GIS.
Manipulation
It is likely that data types required for a particular GIS project will
need to be transformed or manipulated in some way to make them compatible with
your system. For example, geographic information is available at different
scales (street centerline files might be available at a scale of 1:100,000;
postal codes at 1:10,000; and census boundaries at 1:50,000). Before these can
be overlaid and integrated they must be transformed to the same scale. This
could be a temporary transformation for display purposes or a permanent one
required for analysis. There are many other examples of data manipulation that
are routinely performed in GIS. These include projection changes, data
aggregation (for example, to convert sales territories for census building
blocks), and generalization (weeding out unnecessary data).
Management
For small GIS projects it may
be sufficient to store geographic information as computer files. There comes a
point, however, when data volumes become large and the number of users of the
data becomes more than a few, that it is best to use a database management
system (DBMS) to help store, organize, and manage data. A DBMS is nothing more
than computer software to manage a database--an integrated collection of
data.
There are many different designs of DBMS, but in GIS
the relational design has found most favor. In the relational design, data are
stored conceptually as a collection of tables. Common fields in different tables
are used to link them together. This surprisingly simple design has been so
widely used mainly because of its flexibility and very wide deployment in
applications both within and without GIS.
Query
Once you
have a functioning GIS containing your geographic information, you can begin to
ask questions such as:
- Where are all the sites suitable for building new
houses?
- What is the dominant soil type for oak
forest?
- If I build a new highway here how will traffic be
affected?
Both simple and sophisticated queries utilizing more
than one data layer can provide timely information to analysts and managers
alike.
Analysis
GIS
systems really come into their own when they are used to analyze geographic
data. The processes of geographic analysis (often called spatial analysis or
geoprocessing) uses the geographic properties of features to look for patterns
and trends, and to undertake "what if" scenarios. Modern GISs have many powerful
analytical tools, but two are especially important.
- Proximity Analysis
GISs are often
used to answer such questions as
- How many houses lie within 100 m of this water
main?
- What is the total number of customers within 10 km
of this store?
- What proportion of the citrus crop is within 500 m
of the well?
To answer such questions, GIS technology uses a
process called buffering to determine the proximity relationship between
features.
- Overlay Analysis
The integration
of different data layers involves a process called overlay. At its simplest,
this could be a visual operation, but analytical operations require one or more
data layers to be joined physically. This overlay, or spatial join, can
integrate data on soils, slope, and vegetation, or land ownership with tax
assessment.
Visualization
For many types of
geographic operation the end result is best visualized as a map or graph. Maps
are very efficient at storing and communicating geographic information. While
cartographers have created maps for millennia, GIS provides new and exciting
tools to extend the art and science of cartography.
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RESOURCES
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CONTACT INFORMATION
Melvin Barnes
Program Manager
Geographic Information Services
Phone: (407) 665-1105
Fax: (407) 665-7412
E-mail
Information Technology Services
1101 E 1st Street
Sanford, FL 32771
Phone: (407) 665-0311
E-mail
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GIS Tasks